8

Viewing and Changing Normals 161
Smoothing groups define whether a surface is
rendered with sharp edges or smooth surfaces.
Smoothinggroupsarenumbersassignedtothe
faces of an object. Each face can carry any number
of smoothing groups up to the maximum of 32.
If two faces share an edge and share the same
smoothing group, they render as a smooth su rface.
Iftheydon’tsharethesamesmoothinggroup,the
edge between them renders as a corner. You can
manually change or animate smoothing group
assignment. Chang ing smoothing groups does not
alter geometry in any way ; it only changes the way
facesandedgesareshaded.
See also
Viewing and Chang ing Normals (page 1–161)
Viewing and Chang ing Smoothing (page 1–162)
Viewin g a nd Chan ging Nor mal s
When you create an object, normals (page 3–1074)
are generated automatically. Usually objects render
correctly using these default norma ls. Sometimes,
however, you need to adjust the normals.
Left: The normals shown as spikes indicate the orientation
of faces on the pyram id.
Right: Flipping normals can make faces invisible (or visible)
in shaded viewports and renderings.
Undesirednormalscanappearintheseobjects:
• Meshes imported from other applications.
• Geometry generated by complex operations
such as Boolean objects, lathe objects, or lofts.
Normals are used to define which side of a face or
vertex is considered the "out" side. The out side of
a face or vertex is the side that gets rendered unless
you are using two-sided materia ls, or turn on the
Force2-SidedoptionintheRenderScenedialog
> Common panel >
Common Parameters rollout
(page 3–27)
.
Do one of the following to view or change
face
normals
:
•Applya
Normal modifier (page 1–738) .Ifa
Face sub-object selection is active, Normal
applies to the selected faces. If no faces are
selected, Normal applies to the entire object.
•Applyan
Edit Mesh modifier (page 1–613) ,
enable Face, Polygon or Element sub-object
mode, and then use the features on the Surface
Properties rollout to change the directions in
which normals point.
•Converttheobjecttoan
editable mesh (page
1–984)
,enableFace,PolygonorElement
sub-object mode, and use the features on the
Surface Properties rollout
Viewing Normals
The easiest wa y to view normals is to look at an
object in a shaded viewport. In this case, you are
not viewing the normal arrows themselves, but
rather their effects on the shaded sur face. If the
object looks as if it is inside-out, or has holes, then
some of the normals might be pointing in the
wrong direction.
You can display the normal vectors for selected
faces or vertices by enabling Show N ormals on the
Selection rollout of an editable mesh object or the
Edit Mesh modifier.